CWH Underground have published an advisory regarding a malicious file execution vulnerability in WordPress 2.5.1.
We do not quite follow this advisory. The vulnerability discusses the idea of uploading a PHP backdoor onto a WordPress blog via the upload file facility, or via the plugin edit facility. I don’t think this is really a WordPress issue but rather the correct functionality of WordPress.
We have discussed before in our WordPress Whitepaper that the file upload facility should be restricted to trusted users only. We also recommend you reading our Role Management post.